To a perpendicular to the plane of ecliptic, Earth’s axis of rotation makes an angle of 23~ degrees. Had this angle been zero degree, which one among the following would result ?

The Earth's axial tilt of 23.5 degrees relative to the perpendicular of the ecliptic plane is the primary driver of seasonal variations and changes in day length [2]. If this angle were zero, the Sun would remain vertically overhead at the equator throughout the year, effectively creating a permanent equinox state [1]. Consequently, seasons would cease to exist because the variation in solar altitude and intensity across the year would disappear [4]. Furthermore, the circle of illumination would always pass through the poles, ensuring that the length of day and night remains exactly equal (12 hours each) at all times of the year and at all latitudes across the globe [3]. This lack of tilt would eliminate the polar night and the shifting solar declination that currently causes summer and winter [3]. Therefore, all the listed consequences would occur simultaneously.

Sources

1. [1] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 2: The Earth's Crust > THE ALTITUDE OF THE MIDDAY SUN > p. 7
2. [2] Science-Class VII . NCERT(Revised ed 2025) > Chapter 12: Earth, Moon, and the Sun > In a Nutshell > p. 184
3. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 19: The Motions of The Earth and Their Effects > Explanation: > p. 267
4. [4] Science-Class VII . NCERT(Revised ed 2025) > Chapter 12: Earth, Moon, and the Sun > 12.2.2 Seasons on the Earth > p. 177